1. Field of the Invention
The present invention relates to a driving device and an inkjet recording apparatus, more particularly to a driving device for an inkjet recording apparatus which uses an acoustic transducer in the image recording system with liquid ink to supply alternative current signal to a piezoelectric element in order to eject liquid ink, and to an inkjet recording apparatus using the driving device.
2. Description of the Related Art
Inkjet printers, which may record images by ejecting fine particles of ink fluid so-called ink drops onto a recording medium to form dots thereon, have been in practical use. Some inkjet printers are known which make use of the operation of acoustic transducer for the device for ejecting ink drops onto a recording medium.
As an example, there is known technology described in the Japanese Patent Application Laid Open No. 5-278218 corresponding to the U.S. Pat. No. 5,191,354. An inkjet printer using the acoustic transducer may periodical perturbation on the free surface of liquid ink at any appropriate exciting frequency. If the amplitude of the perturbation pressure is more than the level of critical rising oscillation then one or more surface standing waves may be generated on the free surface of the liquid ink to cause to eject the ink drops to the recording medium. In order to generate such perturbation, the transducer may be driven by connecting it to a driver.
Also in the Japanese Patent Application Laid Open No. 8-187853 corresponding to the U.S. Pat. No. 5,589,864, a method using a piezoelectric device driven by RF signal for the transducer is disclosed. This method uses PIN diodes or varactors connected in series to the piezoelectric element to alter the impedance in case of a varactor to switch on and off the RF signal applied to control the ink drops being ejected.
In order to control the RF signal, another method in relation to the RF controller and the RF driver has been proposed by the inventor of the present invention for generating AC signal to the piezoelectric element without using any AC signal power supply (Japanese Patent Application Laid Open No. 11-72211). In this method the inductance connected in parallel to the piezoelectric element constitutes a parallel resonant circuit. A switching means supplies to the piezoelectric element alternatively the electric charge from a charge storage means and the energy from the resonant circuit to eject ink drops, without the need to ever supply AC signals, thereby resulting in the save of power consumed.
To speed up printing, a plurality of ink ejecting mechanisms, i.e., ink-drop ejectors may be provided aligned in one row to allow printing simultaneously in a plurality of positions. Nevertheless, the resulting dots with ink drops ejected by the RF signal may be dispersed. There is a need of restraining such dispersion.
A method has been proposed (Japanese Patent Application Laid Open No. 63-166545) which carries out the pulse-width modulation, amplitude modulation, frequency modulation of the RF signal to alter the size of ink drops. With this method, in other words, the appropriate use of frequency modulation and amplitude modulation as well as pulse-width modulation allows also the dispersion of the size of ink drops to be constant when a plurality of ink pools are provided.
In general, an RF power amplifier of class-A or class-AB is used for the RF controller, i.e., transducer driving circuit. In order to achieve higher speed printing by providing a plurality of ink ejectors as a printing head, a plurality of driver circuits should also be provided, one for each respective ejector. In this condition in the plural drivers the output impedance of the RF power amplifiers is usually 50 xcexa9, the impedance of connecting wires also is 50 xcexa9. In such circuit, the xe2x80x9cQxe2x80x9d of the resonant circuit will become about 1 by the output impedance if the load varies, since the load is much greater than the output impedance. The resonant circuit thereby will be in a forced drive condition (Q less than 1) or the like to prevent frequency shift from occurring when the load capacitance is varied by the printing patterns.
However, it is difficult to hold constant the energy to be transferred to each respective of the printing heads in case of the fluctuation of load, provided that the constant voltage characteristics are ensured in each of printing heads. As a result, it is supposed that the dispersion of energy transferred to each of printing heads may affect to the printing quality. Thus it has been required to prevent the dispersion of energy transferred to each printing head by using frequency modulation, amplitude modulation, and pulse-width modulation as described above.
The frequency modulation, amplitude modulation, and pulse-width modulation, as well as the combination thereof, makes the driver circuit complex and costly.
In addition, inkjet printers have the problem of low efficiency of ink-drop ejection. In other words, driving current is supplied to the piezoelectric elements for producing ink drops, however only a fraction thereof is used for producing ink drops.
When considering that large amplitude is required for the signal input to the switching means for supplying the energy to the piezoelectric element in the inkjet printers, the ejecting efficiency of ink drops is not sufficient if the power consumption for generating input signal is included.
In order to control the ink ejection by turning on and off the RF signal, a switching circuit may be used for switching on and off to control AC signal. On example of AC signal control is the method disclosed in the Japanese Patent Application Laid Open No. 5-318595. In this method, as shown in FIG. 21, a diode switching circuit for controlling a required AC electric signal by applying DC signal to the diode comprises a resistor (Ra1) connected in series with an inductive element (La2) and in parallel to a capacitor (Ca1) as the driving device of inkjet printing head for recording using ink mist. In this circuit, in parallel to the printing head (HEAD), an AC element inductance (La1) is provided at the output side of diode (Da1) but a DC element capacitor is not used in order to minimize the propagation loss of AC electric signal (which is the signal output from an RF amplifier (RFA)).
Also in order to facilitate switching of an amplified RF signal, the method described in the Japanese Patent Application Laid Open No. 10-199995 discloses the RF switching provided with high-voltage CMOS diode.
In this RF switching circuit, RF switching elements such as high voltage diode and varactor are used since RF signal amplified by the radio frequency amplifier circuit has to be switched. As an example, as shown in FIG. 22, in the ink ejector mechanisms (ink-drop emitting mechanisms) arranged in one row for accelerating printing speed, a group of oscillators AcT having a plurality of columns of oscillators may be operated as a printing head. A controller CT for line control is connected at the controller side of each of the plurality of oscillators Ac1 to Acn. A group of circuits ROW having a plurality of column switching circuits are connected at the input side of the plurality of oscillators Ac1 to Acn. Each of the plurality of column switching circuit RW1 to RWn may be selectively operated by the selection signal from the column selection signal output circuit SEL. AC electric signal (signal output from the RF signal source RF and amplified by the RF amplifier RFA) is also input to each of the column switching circuits RW1 to RWn. In this circuit, RF switching elements such as high-voltage diode and varactor are required for the RF signal amplified by the RF amplifier RFA to be switched in each of respective column switching circuit RW1 to RWn.
However in this arrangement the problems of decrease of energy efficiency and degradation of isolation between columns may not be avoided, since the RF signal is switched by the RF switches after amplification, even if such RF switching elements as a high-voltage diode or a varactor are used.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a driving device for inkjet recording apparatus, which uses supersonic waves to significantly save the power consumption, and to allow compact, light-weight, lower price apparatus.
In addition to the above, another object of the present invention is to provide a driving device for inkjet recording apparatus, which may switch on and off at higher speed and lower consumption power for the input signal of small amplitude.
In addition, still another object of the present invention is to provide a driving device for inkjet recording apparatus, which may lower the voltage applied to the RF switches, allowing high frequency amplifier to become more compact without using high voltage elements for the RF switches.
In an inkjet recording apparatus having a plurality of ink drops ejecting mechanisms arranged in a row as a row bank to simultaneously print in a plurality of positions, as printing pattern always changes, the load in the view point of driving device always changes. In the apparatus using supersonic waves for ejecting ink drops, since it has capacitive load, it has been difficult to supply power constantly with respect to the varying capacitance. In the inkjet printing apparatus of the Prior Art uses frequency modulation to keep constant ejection power when the load is changed by modulating frequency based on the load changed due to the printing pattern. On the other hand, a modulation in the driver with transistor switches has been proposed by the inventor of the present invention (Japanese Patent Application Laid Open No. 11-72211).
To simultaneously print in a plurality of positions, power should be effectively supplied to the oscillators such as piezoelectric transducer element. In general high frequency signal is practically used for power supplying to one or more piezoelectric elements. However, high frequency power supplying to one or more piezoelectric elements requires switching with high-voltage element, and may result in some decrease of energy efficiency due to the attenuation of amplified signals, or some degradation of isolation between switched elements.
The first aspect of the present invention is a driving device for an inkjet recording apparatus, wherein AC signals is supplied to a plurality of piezoelectric elements for ejecting liquid ink from at least one piezoelectric element to form an image. The driving device comprises switching means for switching the AC signals for ejecting liquid ink by using selection signals for selecting piezoelectric elements to be supplied with the AC signals to start ejection of the ink, and amplifier means connected to the piezoelectric elements for amplifying the AC signals, wherein the switching means and the amplifier means are connected in series.
In accordance with the first aspect of the present invention, AC signals may be supplied to a plurality of piezoelectric elements while at least one piezoelectric element ejects liquid ink. Among these plurality of piezoelectric elements, some piezoelectric elements may be selected with the selection signal to eject liquid ink, the AC signals may be switched thereto by the switching means so as to eject liquid ink, i.e., so as to be transferred to the selected piezoelectric elements. The AC signals driving the piezoelectric elements are switched first, and then amplified by the amplifier means. The switching means and amplifier means are serially connected to start ejecting liquid ink from the appropriate piezoelectric elements in response to the AC signals applied. In this configuration power may be supplied directly from the amplifier means to the piezoelectric elements so as to prevent amplified signals from attenuating due to the switching by high-voltage switching elements, to avoid the decrease of energy efficiency and the degradation of isolation. By power supplying directly from the amplifier means to the piezoelectric elements, the distance from the piezoelectric elements to the driver means supplying power thereto may be shorter.
Preferably, in an inkjet recording apparatus in which energy for injecting ink from at least one piezoelectric element is supplied for ejecting liquid ink, the driving device for applying AC signals to the piezoelectric elements is disposed such that the distance between the piezoelectric elements and the driving device becomes at or less than 20 times of the wavelength xcex of driving frequency of the piezoelectric elements. In this manner the insertion loss of signal transmission lines and reflection of signal may be minimized, allowing the power to the driving device to be transferred to the piezoelectric elements at the maximum efficiency. Also in this manner the power consumption may be significantly decreased as compared with the coaxial transmission line connection in the Prior Art, as well as the distance between the driving device (especially the amplifier means) and the piezoelectric elements may be shorter, allowing the deployment of more preferable shield which may minimize unnecessary radiation of unwanted electromagnetic waves.
When using a piezoelectric element row bank that constitutes of a plurality of piezoelectric elements, if a plurality of such row banks are placed in parallel in the direction perpendicular to the direction of the row bank, a two dimensional matrix of a plurality of piezoelectric elements may be achieved. The present invention may be preferably applied to such two dimensional matrix of a plurality of piezoelectric elements.
More specifically, a driving device for an inkjet recording apparatus which supplies AC signals to a plurality of piezoelectric elements to eject liquid ink from at least one piezoelectric element to form an image, may comprise: a group of piezoelectric elements including a plurality of piezoelectric element row banks having the plurality of piezoelectric elements arranged in a row for providing a matrix of the plurality of piezoelectric elements; a plurality of switching means, each provided for a respective corresponding row bank of piezoelectric elements, for switching the AC signals including image signals of the image in order to inject liquid ink from the piezoelectric elements; and a plurality of amplifier means each connected to a respective corresponding row bank of piezoelectric elements and each provided between the group of piezoelectric elements and the switching means, for amplifying the AC signals.
The switching means as described above may switch between the row banks of piezoelectric elements having a plurality of piezoelectric elements arranged in a row. In this manner AC signals may be switched first, in the switching means, then supplied to the row banks of piezoelectric elements. By amplifying thus switched and supplied AC signal with the amplifier means, the amplified signals may be directly supplied to the row bank of piezoelectric elements without the attenuation of amplified signal due to the switching, the decrease of energy efficiency, or the degradation of isolation.
If a matrix of a plurality of piezoelectric elements is assumed to be constituted of a plurality of row banks, then the energy (for example, signal voltage) applied to the switching means such as an RF switcher for selecting between row banks of a plurality of piezoelectric elements arranged in a row will become higher. In contrast, in accordance with the present invention, switching means, such as RF switching arrays in typical application for selecting between row banks, may be inserted between the source of AC signal such as an RF signal supply and the amplifier means such as a radio frequency amplifier. This allows the energy applied to the switching means (for example signal voltage) to be lowered, to facilitate selection of a plurality of piezoelectric elements arranged in a row by a row bank signal.
When selecting a row bank of piezoelectric elements for supplying power thereto, it is preferable to select at least one piezoelectric element belonging to the row bank of piezoelectric elements. Accordingly it is preferable for the driving device to further provide driver means for enabling driving of at least one piezoelectric element belonging to the row bank of piezoelectric elements in order to eject liquid ink from at least that one piezoelectric element. In this arrangement AC signals may be switched by the switching means prior to supplying to the row bank of piezoelectric elements, then amplified by the amplifier means to enable at least one piezoelectric element belonging to the row bank of piezoelectric elements so as to facilitate driving of at least one piezoelectric element. Although in this description the elements arranged in a row is referred to as a xe2x80x9crowxe2x80x9d bank, the bank of elements in a row may be referred to as either row or column.
In order to drive piezoelectric elements, both the AC signals and select signals are needed. The switching means may comprise power transistors for amplifying the AC signals, and switching transistors connected in parallel to the power transistors to switch the power transistors between enabled and disabled status. In other words, in the selecting means which may supply AC signals to the amplifier means in response to the selection signal, power transistors may amplify the AC signal, and the power transistors may be enabled or disabled according to the selection signal for selecting a bank of piezoelectric elements. In this manner the switching of AC signal by the selection signal will be easily performed.
More specifically, in the switching means an output node is connected to the drain terminals of P-channel MOS transistor and N-channel MOS transistor, the source terminal of the P-channel MOS transistor is connected to the power supply, the source of the N-channel MOS transistor is grounded to the ground, the gate terminal of the N-channel MOS transistor is connected to the source of AC signal, and the gate of the P-channel MOS transistor is applied with bank (row or column) selection signal to turn on and off the AC signal appeared at the output node.
This power transistor has preferably its output lower than the input threshold of the following amplifier stage in order to suppress erroneous operation. To achieve this, the switching means may incorporate a setting means connected to the input terminal of the power transistor for setting the voltage of AC signal input. By setting the voltage of AC signals, the amplitude of output may be set accordingly. For example, when an amplifier of switching type is used for the high frequency amplifier, erroneous operation (injection error) by the amplifier circuit of the bank of piezoelectric elements currently not selected may be prevented by using MOS transistors to adjust the xe2x80x9coffxe2x80x9d output voltage of the switching means lower than the threshold level of the amplifier means such as radio frequency amplifier switching circuit.
In this setting means a resistor is provided between the gate of N-channel MOS transistor in the switching means and the ground, and between the gate and the power terminal. The value of resistor may be chosen such that the xe2x80x9coffxe2x80x9d output from the switching means may not exceed the input threshold voltage of the amplifier means.
In such configuration as described above, high-voltage switch is useless in the switching means. The source of signals such as RF signal supply for supplying the AC signals is allowed to output low voltage output signal such as TTL- or CMOS-level by means of PLL (Phase Locked Loop) or the like. The selection of column banks in a matrix may be performed by switching the AC signals (RF signals) by the selection signal to feed only to the appropriate column banks of piezoelectric elements. The AC signal (RF signals) input to the selected column bank may be amplified by the amplifier means for that column bank (for example high frequency amplifier-switcher circuit) to apply directly to the piezoelectric element(s). Here at least one piezoelectric element to eject liquid ink is selected by the piezoelectric elements in the row bank selected by the driver means (for example row bank selector circuit) controlled based on the printing pattern.
More specifically, an inkjet printer having a plurality of piezoelectric elements for injecting ink arranged in a matrix, a source of AC signals (RF signal source) for applying to the piezoelectric elements, a column bank switching circuit (RF switch) for switching on and off the AC signals, radio frequency amplifier circuits of the number equal to the column banks, and a row selector circuit for row control based on the printing pattern, may incorporate a column selector circuit for turning on and off the AC signals between the AC signal supply (the source of RF signals) and the radio frequency amplifier.
Also, an inkjet printer having a plurality of piezoelectric elements for injecting ink arranged in a matrix, a source of AC signals (RF signal source) for applying to the piezoelectric elements, a row bank switching circuit (RF switch) for switching on and off the AC signals, radio frequency amplifier circuits of the number equal to the row banks, and a selector circuit for column control based on the printing pattern, may incorporate a row selector circuit for, turning on and off the AC signals between the AC signal supply (the source of RF signals) and the radio frequency amplifier.
Any switching type amplifier may be served for the radio frequency amplifier circuit. The transistors configured fur the switching means may also be served for the row selector circuit or the column selector circuit. In this case the parameter of N- and P-channel MOS transistors (on resistance and the like) may be selected such that the xe2x80x9coffxe2x80x9d output from the row selector or column selector circuit will not exceed to the input threshold voltage of the radio frequency amplifier switching circuit. More specifically, resistors are provided between the gate of N-channel MOS transistor of the row or column selector circuit and the ground and between the gate and the power supply, the value of the resistors being determined such that the off output of the row or column selector circuit may not exceed the input threshold of the radio frequency amplifying switching circuit.
In a matching scheme with an inductance inserted in parallel to the oscillator capacitance or in a drive using the resonance for yielding the maximum power transferred to the oscillator, when the load varies the frequency may be shifted if the inductance for the resonance circuit is fixed.
In order to overcome this problem, the second aspect of the present invention is a driving device for an inkjet recording apparatus, wherein the frequency shift is suppressed by the printing pattern. For example, an arrangement having an inductance for the resonance with respect to the loads driven simultaneously, and a series CR circuit in parallel to the parallel LC equivalent circuit (TANK circuit).
Specifically, the second aspect of the present invention supplies AC signals to a plurality of piezoelectric elements while injects liquid ink from at least one piezoelectric element to form an image, comprises an inductance connected in parallel to the plurality of piezoelectric elements, switching control means for controlling injection of the liquid ink by switching on and off the connection between the plurality of piezoelectric elements and the AC signals, and an adjusting means for holding resonant frequency to a predetermined value by controlling the resonant frequency in response to the changes of capacitive load of the plurality of piezoelectric elements.
The second aspect of the present invention may supply AC signals to a plurality of piezoelectric elements while injects liquid ink from at least one piezoelectric element. An inductance is connected to these plurality of piezoelectric elements. The inductance and the piezoelectric element may form a resonant circuit. When AC signals are supplied to the piezoelectric elements, the resonant circuit will accumulate an amount of energy.
The switching control means controls the injection of liquid ink by switching on and off the connection between a plurality of piezoelectric elements and the AC signals in response to input signals. When the signals are switched on or off by a switching element such as transistors, if the switching is on, the AC signals will be supplied to the piezoelectric elements. At this time some energy will be saved in the resonant circuit. If the switching goes off, the energy accumulated in the resonant circuit will be supplied to the piezoelectric elements. The energy from AC signals and the energy from the resonant circuit will be alternatively supplied to the piezoelectric elements to oscillate the liquid ink to start ejecting the ink.
In this case, if the number of driven elements in the plurality of piezoelectric elements is changed, the capacitive load will be altered accordingly. The adjusting means adjusts the resonant frequency in response to the amount of shift of the capacitive load of the plurality of piezoelectric elements to control the resonant frequency to a predetermined value. This allows some energy to be supplied at a predetermined fixed resonant frequency by the adjustment of the adjusting means if the capacitive load is varied due to the changes of the number driven of the plurality of piezoelectric elements.
The input signals may use the printing pattern to form an image. By using the printing pattern (drive signal indicating the position of the piezoelectric elements to be driven corresponding to the image data) for the input signals, liquid ink may be driven in a manner approximately uniform at every piezoelectric element, and printed dots also may be approximately uniform each other, resulting in an image of higher quality.
For the adjusting means, an LC circuit of an inductor and a capacitor connected in parallel may be used. The inkjet recording apparatus of the present invention incorporates an LC circuit comprised of the capacitance of piezoelectric elements and a fixed inductance. An additional LC circuit is connected in parallel to the LC circuit of the capacitance of piezoelectric elements and a fixed inductance to compensate for the fluctuating load, including its complex component, so as to regulate to a constant frequency. The LC circuit additionally connected in parallel supports the complex component that may lack with respect to the driving frequency when the capacitance fluctuates according to the printing pattern. Consequently a constant frequency may be regulated.
A limiting resistor may be further serially connected to the above additional LC circuit connected to the LC circuit comprised of the capacitance of piezoelectric elements and a fixed inductance. By using this, the amount of charges in the added LC circuit may be maintained to a constant level, while on the other hand the limiting resistor may always keep constant the amplitude of voltage of the transferred signal at the time of fluctuating capacitance.
When an additional LC circuit is added in parallel to the LC circuit comprised of the capacitance of piezoelectric elements and a fixed inductance, these two inductances may be degenerated to only one inductance because they are connected in parallel. Therefore, an RC circuit of a resistor and a capacitor serially connected may be used for the adjusting means. This means that since the inductance in the additional LC circuit and the fixed inductance may be degenerated to only one inductance, when degenerated, the additional LC circuit may be thought to be merely a C. If the limiting resistor is serially connected to this degenerated LC circuit, the resulting circuit will be equivalent to an RC circuit, which may safely omit an inductance without decrease of performance.
In order to preferably regulate the varying capacitive load in response to the printing pattern, some voltage controlling elements such as variable capacitors and variable inductors may be used. When using a variable capacitative element, that is, when the adjusting means includes a voltage controlling element, the capacitive fluctuation due to the printing pattern may be compensated for and a constant load to the sender may be achieved by controlling the voltage controlling element with an element controller means in response to the fluctuating capacitive load of the plurality of piezoelectric elements.
One variable capacitative element is, for example, a voltage controlled variable capacitative element by the voltage regulated by a variable capacitance diode and the like. When using a variable capacitor, that is, when the adjusting means includes a variable capacitative element, the adjusting means may vary its capacitance in response to the fluctuation of capacitive load of the plurality of piezoelectric elements. As can be seen, the voltage regulated variable capacitative element may compensate for the fluctuating capacitance due to the printing pattern and regulate a constant load to the sender circuit.
If the signal applied to the voltage regulated variable capacitative element has an amplitude larger than the variable capacitance controlling voltage, then the range of varying capacitance will be narrowed, and the regulation of capacitance to a target value may or may not be difficult. In such a case, a voltage regulated variable capacitative element such as variable capacitance diode may be provided to each of respective positive and negative voltages sides to connect the one""s cathode with the other""s anode to apply both positive and negative voltages. In this manner the sum of capacitances of variable capacitance diodes i.e., voltage controlled variable capacitative elements may be held to a constant value for AC signals, allowing capacitance to be electrically controlled.
Another example of voltage controlling element is a variable inductance element. When the adjusting means comprises a variable inductance element, it can vary its capacitance in response to the fluctuation of capacitive load in the plurality of piezoelectric elements. As can be appreciated, by completing fluctuating capacitance due to the printing pattern with a variable inductance element the frequency may be always held to a constant value. In other words, when the capacitance varies in response to the fluctuation of capacitive load in a plurality of piezoelectric elements, if the inductance value corresponding to the fluctuation may be determined, the variable inductance element may compensate for it. This allows fluctuating inductance due to the printing pattern to be varied according to the fluctuating capacitance to always hold a constant frequency.
In the second aspect of the present invention, the adjusting means may further provide a power detector means for detecting the supplied power of the supplied current or supplied voltage to the piezoelectric elements, and a power controller means for regulating the resonant frequency in response to the detected power.
The controllable value for controlling the voltage controlling element, i.e., the voltage for controlling the voltage controlled variable capacitative elements or the voltage for controlling the voltage controlled variable inductance element can be calculated in advance based on the printing pattern, the magnitude of load being the product of the number of printing dots and the capacitance of each respective oscillator. When the supplier provides constant voltage or constant current characteristics, the controllable value may be determined by using the relationships of the printing pattern proportional to the supplied power, i.e., supplied voltage or current from the supplier to detect the applied power, i.e., current or voltage.
The second aspect of the present invention may be used in combination with the first driving device in accordance with the present invention. When used in combination, the combination may be achieved by coordinating the controller switching means included in the second driving device to the switching means included in the first driving device to constitute a driving device having further inductances and adjusting means.
The third aspect of the present invention is a driving device for inkjet recording apparatus for achieving the above objects, which supplies AC signals to a plurality of piezoelectric elements to eject liquid ink from at least one piezoelectric element to form an image, may comprise: inductances connected in parallel to the plurality of piezoelectric elements to form a resonant circuit, first switching means for controlling the connection between the plurality of piezoelectric elements and the AC signals, resonant circuits connected in parallel to the first switching means, second switching means for controlling supply of the AC signals to the resonant circuits, and controller means for controlling injection of the liquid ink by causing the second switching means to be iteratively repeated to be turned on; and off in response to the signal input thereto.
The third aspect of the present invention may supply AC signals to a plurality of piezoelectric elements while injecting liquid ink from at least one piezoelectric element. Each of the plurality of piezoelectric elements is connected in parallel to an inductance to form a resonant circuit. When AC signals are fed to the piezoelectric elements, energy will be accumulated in the resonant circuits.
The controlling means controls the injection of liquid ink by switching on and off the connection between the plural piezoelectric elements and the AC signals in response to the input signals. In other words, when the first switching means switches on or off, if on then the AC signals will be fed to the piezoelectric element. At the same time some energy of signals may be accumulated in the resonant circuit. When the first switching means is off, the energy saved in the resonant circuit will be supplied to the piezoelectric element. The first switching means may be connected in parallel to a resonant circuit, to which AC signals from the second switching means will be supplied. When the second switching means operates to switching on or off in response to the input signal such as printing pattern and the like, if switching on, then some energy will be accumulated into the resonant circuit. Also if the second switching means is turned off, then the energy saved in the resonant circuit will be supplied to the first switching means. Therefore AC signals and energy from the resonant circuit will be alternatively fed to the first switching means to start oscillating and injecting liquid ink.
For example, the inkjet recording apparatus to which the present invention is applicable may supply AC signals to piezoelectric elements acoustically coupled to liquid ink (generate acoustic signals) to inject ink. The piezoelectric elements may be connected to a multi-stage switching means for controlling the connection between the input signals and the piezoelectric elements. The multi-stage switching means may be capacitive coupled to the conductance.
Between stages of respective switching means, an inductance and a resistance are connected between the output node of a switching means and the ground. The inductance and resistance forms a parallel resonance circuit with respect to the composite capacitance of the output capacitance of preceding switching means with the input capacitance of succeeding capacitance.
The value of inductance may be set according to the composite capacitance and the frequency of input signals. The input signals are assumed to be burst pulses in the range between 100 and 200 MHz. It should be noted that a sinusoidal burst wave may be used instead.
The value of resistance may be set so as to settle the sharpness of the parallel resonant circuit xe2x80x9cQxe2x80x9d to be a desired value (for example, preferably 1 to 2). This is for the wave shaping of rising and falling edges of the RF signal part in the burst signals.
When using high speed, small input capacitance, and small output switching means having the parallel resonant circuit as described above for the first stage, if the initial input signal is of small amplitude, for example burst pulses at TTL level of 0 to 5V, the first stage may supply sinusoidal waves of larger amplitude oscillating from 0V to both positive and negative sides.
In addition, by applying the same technique, i.e., driving succeeding stage of switching means having larger output and larger input capacitance, the piezoelectric elements may ultimately be driven by the signals of desired amplitude.
More specifically, the resonant circuit and the first switching means may be capacitive-coupled with a capacitor or the like.
The resonant circuit may also comprise an inductance for resonance, which may constitute a parallel resonant circuit having the composite capacitance of the output capacitance of second switching means connected to the input of resonant inductance with the input capacitance of first switching means connected to the output of resonant inductance, and the composite impedance of the output impedance of second switching means connected to the input of resonant inductance with the input impedance of first switching means connected to the output of resonant inductance.
This parallel resonant circuit may be tuned to the input signals. The resonant circuit may be of an inductance element and a resistor. The resistor may form a parallel resonant circuit comprised of the inductance element, and the composite capacitance of the output capacitance of second switching means connected to the input of the inductance element with the input capacitance of first switching means connected to the output of the inductance element.
The resistor value R in this case may be preferably set to be in the range xcfx80xc2x7Fxc2x7L less than R less than 2xcfx80xc2x7Fxc2x7L, where L is the value of the inductance element, F is the resonant frequency of the parallel resonant circuit.
The input signals may preferably be low voltage signals within a predetermined range (so-called TTL level) and may preferably be a sort of pulse signals.
The third aspect the present invention may be combined with at least one of the first and second driving devices. When combining it with the first driving device in accordance with the present invention, the combination may be achieved by coordinating switching means included in the first driving device in accordance with the present invention with the first switching means and the second switching means of the third driving device in accordance with the present invention to further provide inductances and controlling means for the driving device. When combining with the second driving device in accordance with the present invention, the combination may be achieved by coordinating controller switching means included in the second driving device in accordance with the present invention with the first switching means and second switching means of the third driving device to further provide inductances and controlling means for the driving device.